qemu: enable host support for armsr/armv8

qemu: enable host support for armsr/armv8

As of OpenWrt main branch commit e505873e65f72 ("armsr: armv8:
enable KVM host") [merged 2023-08-15], armsr/armv8 has
KVM host support. We can now enable QEMU host for this
target.

For example, you can run OpenWrt armsr/armv8 as a guest
like so:
qemu-system-aarch64 -nographic -M virt -cpu host --enable-kvm \
	-bios u-boot.bin -smp 1 -m 1024 \
	-drive file=openwrt-armsr-armv8-generic-ext4-combined.img,format=raw,index=0,media=disk

A compatible u-boot.bin can be obtained from u-boot-qemu_armv8/u-boot.bin
that is built with the armsr target and available from
downloads.openwrt.org.

Signed-off-by: Mathew McBride <matt@traverse.com.au>